Ultrasonic imaging device

ABSTRACT

An ultrasonic imaging device comprising a transmitting transducer which is rectilinearly arranged and which transmits acoustic waves of input signal frequencies to a target object in directions corresponding to said frequencies, an acoustic lens which converges reflected acoustic waves from said target object, and a receiving transducer which is divided in a direction orthogonal to the scanning direction of said acoustic lens, each divided part constituting a receiving element, and which receives the acoustic waves converged by said acoustic lens.

United States atent 1191 1111 3,794,964 Katakura Feb. 26, 1974ULTRASONIC IMAGING DEVICE 2,528,730 11 1950 Rines 340/ MP 1751 InventKageyoshi Katakurwokywapan 232318;? 513350113i???:::...............;':;::..ilfi [73] Assignee: Hitachi, Ltd.,Tokyo, Japan Filed: y 1972 Primary ExaminerRichard A. Farley Appl. No.:256,849

Attorney, Agent, or FirmCraig and Antonelli [57] ABSTRACT An ultrasonicimaging device comprising a transmitting transducer which isrectilinearly arranged and which transmits acoustic waves of inputsignal frequencies to a target object in directions corresponding tosaid frequencies, an acoustic lens which converges reflected acousticwaves from said target object, and a receiving transducer which isdivided in a direction orthogonal to the scanning direction of saidacoustic lens, each divided part constituting a receiving ele- [56] Refeen Cit d ment, and which receives the acoustic waves con- UNITED STATESPATENTS verged by said acoustic lens.

3,419,845 12/1968 Thiede et a]. 340/3 FM 9 Claims, 17 Drawing Figures 30TRANSMITTING PART 3| 32 TRANSMITTING TRANSMITTING i g E7 POWER AMPL I L6 /5O DISPLAYING PART 42 42 4I BRIGHTNESS CATHODE- l ANALOG FREQ E RAYTUBE a I SWITCH ANAL ZE E PRE AMP L 52 e0 --PII P17 /44 Psw FREQ SWEEPPR GEN L V Y A 1 I 40 RECEIVING PART OSCILLATING 8- FREQ l DIVID'NGCONTROLLING PART DEVICE PAIEmfn iazsisn SHEET 1 BF 6 TRANSMITTERFREQUENCY ANALYZER FIG.3

INPUT FREQUENCY (MHZ) PATENTED 3.794. 964

sum 2 OF 6 ACOUSTIC PRESSURE x 30cm m m w o u n mmnwwwmm 2582 as lcm lMHz FIG. 8b

5 m 5 a O Y DIRECTION POSITION (cm) 62 wmnmmuE 0 58% X DIRECTIONPOSITION (cm) PATENTED 3.794.964

SHEET 5 (IF 6 FIG. l4

eo| W -2 Go-N W i Ts PR J I ULTRASONIC IMAGING DEVICE BACKGROUND OF THEINVENTION:

The present invention relates to an ultrasonic imaging device which,using ultrasonic waves, picks up an object image by reflected ultrasonicwaves from an object present in the water, etc.

DESCRIPTION OF THE PRIOR ART:

Among methods of detecting the configuration of a target object in, forexample, opaque water, there have heretofore been a type in whichultrasonic waves are radiated from a transmitting transducer, and thewaves reflected from the target object are focused into an image onto areceiving transducer consisting of a number of receiving elementsarranged in a planar array through an acoustic lens, to thereby obtainan object image. The receiving transducer of another type may consist ofa number of receiving elements arranged in a linear array andmechanically displaced, to thereby obtain an object image extending inthe form of a plane.

However, in the former case of using the receiving transducer with thereceiving elements disposed in a planar array, selecting the position ofthe receiving elements is difficult, and the device becomes verycomplicated. In the latter case of rectilinearly arranging the receivingelements and mechanically moving them for scanning, the speed is limitedby the mechanical movement, and the imaging speed may not be made high.Thus disadvantages have occurred in the prior art.

As wave transmitting means, there has been employed a method throughwhich the entire area of a target object is irradiated by means of asingle transmitting element, and a method in which transmitting elementsarranged in a planar array aremechanically displaced to irradiate anobject. However, the former has been disadvantageous in that thereflection efficiency is very poor, while the latter has beendisadvantageous in that the irradiation speed may not be made high.

SUMMARY OF THE INVENTION:

A principal object of the present invention is to provide an ultrasonicimaging device which is simple in construction and which may carry outhigh-speed imaging.

Another object of the present invention is to provide a device in whichposition selection for receiving elements is made easy.

Still another object of the present invention is to provide a device inwhich the reflection efficiency is excellent.

Yet another object of the present invention is to provide an ultrasonicimaging device whichhas good range resolution.

In order to accomplish such objects, the present invention isconstructed so that ultrasonic waves are radiated from a transmittingtransducer which is rectilinearly arranged and which sends outultrasonic waves of respective input frequencies in directionscorresponding to the input frequencies, and that reflected waves from atarget object are converged by an acoustic lens and received as an imageby a receiving transducer which is divided in a direction orthogonal tothe scanning direction of the ultrasonic lens.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a diagram showing the construction of an embodiment of theultrasonic imaging device according to the present invention;

FIG. 2 is a diagram for explaining the construction and operation of atransmitting transducer;

FIG. 3 is a graph showing the relation between the input frequency andthe acoustic-wave transmitting direction in the transmitting transducer;

FIG. 4 is a diagram showing the state in which acoustic waves radiatedfrom the transmitting transducer are spread;

FIG. 5 is a diagram showing an example in which an acoustic lens isjointly used for the transmitting transducer;

FIG. 6 is a diagram showing an example in which the transmittingtransducer is curved;

FIG. 7 is a diagram showing concrete numerical values of various partsof an embodiment of the present invention;

FIGS. 8a and 8b are diagrams respectively showing the relationshipsbetween the positions in the x-axial and y-axial directions on thesurface of a target object and acoustic pressure;

FIG. 9 is a diagram showing an example of changesver sus time of thetransmission frequency;

FIG. 10 is a diagram for explaining changes-versustime of the wave frontpositions of the transmitted acoustic waves;

FIG. 11 is a diagram showing the relation between changes-versus-time ofthe transmission frequency and the reception frequency;

FIG. 12 is a diagram showing the construction of an other embodiment ofthe ultrasonic imaging device according to the present invention;

FIG. 13 is a diagram showing the practical construction of a frequencyanalyzer in FIG. 12;

FIG. 14 is a time chart of signals at various parts in FIG. 12;

FIG. 15 is a diagram showing the practical construction of a controlsection in FIG. 12; and

FIG. 16 is a time chart of signals at various parts in FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION:

FIG. 1 shows an embodiment of the ultrasonic imaging device according tothe present invention, in which numeral 1 designates a transmitter fortransmitting signals of various frequencies. Numeral 2 indicates atransmitting transducer which radiates ultrasonic waves in therespectively predetermined directions corresponding to the frequenciesof the signals applied from the transmitter l, and which is constructedas shown in FIG. 2.

More specifically, a number of transmitting elements 3 made of titanium,lead zirconate, etc, are arrayed in the AB-direction. The directions ofpolarization of the respective transmitting elements are selected so asto be orthogonal to the arrayed direction AB of the transmittingelements and to be alternately polarized as illustrated at arrows 4.Further, common electrodes 50 and 5b are respectively mounted on theupper and lower surface of the transmitting elements. With such aconstruction, when an input signal is applied from the transmitter 1 tothe common electrodes 5a and Sb, acoustic waves are sent out in theABCD-plane and in the OH direction inclined at an angle 6 with respectto a straight line OG normal to the electrode plane, and the directionOH varies dependent upon the input frequency. For example, when an inputhaving a frequency f is applied from the transmitter l, acoustic waveshaving the frequency f are sent out from the transmitting transducer 2in the direction OH which is determined by the input frequency. As theinput frequency fis varied, the angle 6 varies, and the sent-outdirection OH of the acoustic waves changes in the ABCD-plane.

Referring again to FIG. 1, numeral 6 designates a target object, 7 anacoustic lens for converging reflected acoustic waves from the targetobject 6, and 8 a receiving transducer for receiving the acoustic wavesconverged by the acoustic lens 7. The wave receiving surface of thereceiving transducer 8 is divided into a number of elongated parts in adirection orthogonal to the scanning direction of the acoustic waves,and each divided wave-receiving surface constitutes a receiving element9. Numerals l and 12 indicate selecting switches, while numeral 11 is afrequency analyzer.

With such a construction, when an input signal is applied from thetransmitter 1 to the transmitting transducer 2, acoustic waves are sentout from the transmitting transducer 2 in a direction corresponding tothe frequency of the input signal. FIG. 3 is a graph which shows therelation between the input frequency and the acoustic-wave transmittingdirection. As can be understood from the graph, the transmittingdirection changes with changes in the input frequency. The acousticwaves thus sent out are irradiated on the target object 6. In this case,the acoustic waves of the individual frequencies are irradiated on thex-axially elongated surfaces of the target object 6 as at 6a, 6b and 6c,and the irradiated surfaces change in the y-axial direction in the orderof, e.g. 6a, 6b, 6c with corresponding changes in the frequency. Theacoustic waves reflected by the target object 6 are converged by theacoustic lens 7, and are focused into an image on the wave receivingsurface of the receiving transducer 8. Accordingly, the position ofreflection also changes in the yaxial direction, i.e., in the verticaldirection on the drawing, in dependence upon the applied frequency inthe receiving transducer 8. For this reason, the receiving transducer 8is divided into a plurality of parts in the x-axial direction, i.e., inthe horizontal direction, and each divided part consists of thereceiving element 9. Outputs of such respective receiving elements 9 aresequentially changed-over by the selection switch 10 and applied to thefrequency analyzer 11, where they are subjected to frequency analysis,and outputs, respectively corresponding to the frequencies, are selectedand delivered by the selection switch 12. Thus, the output frequency ofthe transmitter l is sequentially changed and the outputs of thefrequency analyzer 11 are changed over by the selection switch 12 so asto conduct scanning in the y-axial direction, and the outputs of therespective receiving elements are changeover by the selection switch 10so as to conduct scanning in the x-axial direction, whereby outputs fora twodimensional ultrasonic acoustic image of the target object 6 may beobtained.

Consequently, the selection of the two-dimensional positions of thetransmitting elements is unnecessary in the present invention, and thedevice may be constructed extremely simply. In addition, since imagesare picked up by the frequency sweep, both the transmitting andreceiving transducers need no mechanical scanning, so that the imagingspeed may be made sufficiently high. Furthermore, since the x-axiallyelongated surface is irradiated with acoustic waves at a time by meansof the transmitting transducer arranged rectilinearly, the reflectionefficiency from the target object is very high, and the output of thereceiving transducer is increased to that extent.

While the foregoing is satisfactorily applicable to cases where thetarget object is comparatively distant, it is not necessarilyapplicable, as illustrated in FIG. 4, in the case where the targetobject is at a short distance.

More specifically, acoustic waves of a certain frequency radiated fromthe transmitting transducer 2 travel in the form of plane waves 13 for awhile, and gradually become spherical waves 14. Therefore, although thedirectional angle a as viewed from the transmitting transducer 2 issmall and the bearing resolution is high for the distant target object,the directional angle 11 increases and the bearing resolution decreasesfor an object disposed a short distance away.

Therefore, as shown in FIG. 5, an acoustic lens 15 is provided in frontof the transmitting transducer 2 so as to focus acoustic waves radiatedfrom the transmitting transducer. Thus, an equivalent resolution to thatof the distant case may also be obtained for the object at a shortdistance.

The directional angle may also be made small in such a way that, asshown in FIG. 6, the transmitting transducer 2 itself is arranged in acurved form to thereby focus the acoustic waves.

In the foregoing embodiments, it has been assumed that all the acousticwaves sent out from the transmitting transducer are of one frequencycomponent, that the frequency is successively varied, and that thedirection of the transmission from the transmitting transducer is alsovaried in succession by the frequency, so as to scan a target. It isalso possible, however, that a noise frequency input containing a numberof frequency components is applied to arrayed transmitting transducersinstead of making the input frequency of the transmitting transducer onefrequency component, whereby acoustic waves of frequencies respectivelycorresponding to various directions are simultaneously sent out. Whenthe noise frequency input of frequency components in a frequency rangecapable of covering a required field of view is applied to the arrayedtransmitting transducers, acoustic waves in the abovementioned frequencyrange are simultaneously transmitted over the entire area of therequired field of view. Reflected waves of the respectively differentfrequencies are focused on the receiving transducer from various partsof the target object, and a two-dimensional acoustic image is formed onthe wave receiving surface.

In order to thus obtain the acoustic image, a device quite similar tothat in FIG. 1 may be used.

On the other hand, if a frequency analyzer is provided for everyreceiving element in place of the single frequency analyzer 11 in FIG.1, so as to simultaneously subject the outputs of the respectivereceiving elements to the frequency analysis and to thereby obtain theoutputs of the respective frequencies, then the images of arbitrarypositions of the target object will advantageously be immediatelyobtained.

In that case, the selector switch is omitted.

Now, numerical values of an embodiment of the device according to thepresent invention will be discussed in connection with FIG. 7.

In this case, the transmitting elements 3 each being about 1 mm wide andabout 0.9 mm thick are arranged in a straight line to constitute thetransmitting transducer 2 being about l5cm long. In front of thetransmitting transducer 2, acoustic lens 15 is disposed one side ofwhich is about 30cm long and the focal distance is about 50cm. Acousticwaves are irradiated on a target object which is about 50cm from theacoustic lens 15. It is assumed that the frequencies at this time are ofa single sinusoidal wave in a frequency range from about 1 MHZ to1.5MHZ, while the output of the transmitter is approximately 1W.

The directional characteristics of the acoustic pressure of the acousticwaves irradiated on the target object, in this way, roughly have therelationship shown on the right side in FIG. 7, and concretely are asshown in FIGS. 8a and 8b. More specifically, FIGS. 80 and 8!) illustrateacoustic pressures in the x-axial and y-axial directions of the targetobject when signals of the frequency IMHz are irradiated. It isunderstood from the diagrams that the radiated acoustic waves havedirectivities to specific positions as correspond to the fre quency.

In case where noise frequency inputs containing a number of frequencycomponents as have been previously stated are simultaneouslytransmitted, directional characteristics quite similar to those in FIGS.8a and 8!; may also be obtained.

Since the foregoing embodiments have no range resolution, it is fearedthat scattered acoustic waves from air bubbles etc. being much existentin the water are simultaneously received as jamming waves, to render animage unclear.

Description will be hereunder made of another embodiment of the presentinvention in which such a disadvantage is eliminated and rangeresolution is provided.

In the present invention, frequency-swept acoustic waves having theirfrequency varied with time are sent out from the transmittingtransducer. Now, let us consider a case where the relation between thetransmission frequencies of the frequency-swept acoustic waves and timeis repeatedly changed, as shown in FIG. 9, in the form of saw-toothwaves from a frequency f to a frequency f, with the lapse of time t.

In this case, as the time proceeds from 1 via +A, t 2A to 1,, A, thetransmission frequency varies from f via f f to j}, The state in whichsuch frequency-swept acoustic waves are sent out from the transmittingtransducer is as illustrated in FIG. 10. Since the distance between thetransmitting transducer 2 and the acoustic lens US for the wavetransmission is almost negligible, the acoustic waves sequentially'varythe transmitted direction about the acoustic lens and in correspondencewith the frequencies with the lapse of time, and are sent out indirections respectively determined by the frequenciesf f, f f.,. In thefigure, C signifies the propagation velocity of the acoustic waves inthe water.

The position of a wave front after the acoustic waves of the frequencyf, have been thus transmitted, that is, at time t t 'r is shown by acurve 21 in the figure. As apparent from the curve, an object which, byway of example, is located in the transmission direction of the acousticwaves of the frequency 1], and exists at point A on the curve 21 issubjected to the acoustic wave irradiation of the frequency f and sendsout reflected waves at the time t t r. A propagation period of timerequired for the reflected waves to reach the wave receiving surface ofthe receiving transducer (not shown) placed in the vicinity of thetransmitting transducer 2 is 'r, so that the reflected waves of the frequency 11, from the point A are received at time:

Letting the position of a wave front at time t t r A be represented by acurve 22, an acoustic wave at the frequencyf impinges upon point B at tt 'r A, this point being located in the transmitted direction of theacoustic waves of frequency f and on the curve 22. Reflected waves reachthe wave receiving surface of the receiving transducer at time:

As apparent from FIG. 9, A signifies the period of time in which thetransmission frequency varies from )2, to f,.

Similarly, among waves reflected from an object which is located at adistance C 1' from the position of the transmitting transducer, those ofthe frequency f,, (where n O, l, 2, 5) are received at time t t 2 r n A.Letting the wave-front positions of the acoustic waves at times t 'r andt 'r' A be represented by curves 23 and 24, waves reflected from objectsA, B, C', located at a distance C from the transmitting acoustic lens 15are received as signals of the frequency f, at times t t 2 'r' n A.

In this manner, reflected waves from objects being at respectivelydifferent distances from the transmitting acoustic lens 15 are obtainedin the form of signals which differ in time and frequency. Outputs corresponding to the reflected waves from the objects on planes respectivelybeing at distances corresponding to various delay times may therefore beseparated and derived in such way that, as illustrated in FIG. 1 l, thecenter reception frequency of the receiver as shown by the dotted lineis varied similarly to the transmission frequency shown by the solidline, but with a delay of a period of time D, and that the delay time Dis further varied. While the foregoing is a description of the singlereceiving element with the divided wave-receiving surfaces, it is to beunderstood that a two-dimensional image pickup having range resolutionmay also be carried out by approximately disposing each receivingelement.

Considering that the frequency is determined in correspondence with abearing and that the delay time is determined in correspondence with adistance to a target plane, it is to be understood that the image pickupof an arbitrary plane is possible by suitably selecting the delay time Dof the center reception frequency in FIG. 1 1.

Next description will be made of a practical device to be used therefor.FIG. 12 is a block diagram showing an embodiment of the device accordingto the present invention, which is composed of a transmitting part 30, areceiving part 40, a display part 50 and a control part 60.

In the transmitting part 30, reference numeral 31 designates afrequency-swept wave generator for wave generation, while 32 is a poweramplifier for wave transmission. In the receiving part 40, referencenumeral 41 indicates a pre-amplifier, 42 a frequency analyzer, 43 ananalog switch, and 44 a frequency-swept wave generator. In the receivingsection 50, reference numeral 51 represents an amplifier for brillancemodulation, while 52 is a Braun tube. In the control part 60, referencenumeral 61 shows an oscillator and frequency divider.

Parts 2, 6, 7, 8 and are the same as those of identical numerals shownin FIG. 1 and FIG. 5.

With such construction, the transmitting frequencyswept wave generator31 of the transmitting part 30 is driven by sweep synchronizing pulsesP, having a period T, as sent out from the oscillator and frequencydivider 61 of the control part 60. Thus, a frequencyswept signal ehaving a period T, and a frequency range f f is obtained. It isamplified by the transmitting power amplifier 32, and is applied to thetransmitting transducer 2. Acoustic waves sent out from the transmittingtransducer 2 permeate through and are converged by the transmittingacoustic lens 15 to be irradiated on the target plane 6.

Waves reflected from an object at the target plane 6 are converged bythe receiving acoustic lens 7, and are focused into an image on the wavereceiving surface of the receiving transducer 8. Outputs of therespective receiving elements generated thereby are amplified by thepre-amplifier 41 in the receiving section 40. An output signal e of thepre-amplifier 41 is applied to the frequency anaylzer 42.

FIG. 13 illustrates the construction of the frequency analyzer 42corresponding to one channel. It comprises a mixing circuit 45, aband-pass filter 46 and a low-pass filter 47.

The output signal e has its frequency converted by a frequency-sweptcarrier signal e in the mixing circuit 45, only a predeterminedband-width component is selected and passed by the band-pass filter 46,and only a lower frequency component is passed by the low-pass filter47. The envelope wave component thus obtained is derived as an outputsignal e of the frequency analyzer 42.

Herein, the frequency-swept carrier signal e is obtained by driving thefrequency-swept wave generator 44 by sweep synchronizing pulses P whichare delayed by a delay time D with respect to the sweep synchronizingpulses P,. It is a frequency-swept signal having a period T, and havinga frequency range f to f Be tween the frequencies of thepreviously-mentioned frequency-swept signal 2,, and the above-mentionedfrequency-swept carrier signal e there is the following relation:

flu. fin. fRH fs'n f0 The center frequency of the band-pass filter 46 ofthe frequency analyzer 42 is made the frequency difference fl,, wherebywaves reflected from a distance corresponding to the delay time D may bederived.

Subsequently, the outputs of the frequency analyzer 42 are changed-overby the analog switch 43. The output thereof is amplified and brightnessmodulated by the amplifier 51 for brightness modulation. Further, thedeflecting means (not shown) of the Braun tube 52 are driven byhorizintal synchronizing pulses P at a period T and and verticalsynchronizing pulses P at a period Ty. Thus, the object image isdisplayed in the form of brilliance or brightness changes of scanninglines in the vertical direction of the Braun tube 52.

This state is as illustrated in a time chart in FIG. 14 where e,designates the output of a channel i of the frequency analyzer, whileGATE i indicates sampling pulses of the frequency analyzer output 0,, iof the channel i. Reference character N signifies the number of thedivisions of the wave receiving surface, namely, the number of receivingelements. In the analog switch 43, the sampling number of each analyzeroutput within one sweep period T is assumed to be M. The samplingperiod'T, of the analyzer output e,,, accordingly, becomes:

In the analog switch 43, in order to change-over N channels within onesampling period, i.e., T the change-over period T of analog switchcontrol pulses P is:

The vertical synchronization period T in the display part 50 has therelationship T T The period T of the horizontal synchronizing pulses Pin the display section has the relationship T T while their phase isequal to that of the sweep synchronizing pulses P The number of frames Fhas the relation of F l/T Further, with the method as will now beexplained, the timing relation between the sweep synchronizing pulses P,and the sweep synchronizing pulses P delayed by the period of time Dover the former, or the delay time D, is varied, whereby the image ofreflected waves from an optical distance is brilliance-modulated anddisplayed on the Braun tube at the number of frames F FIG. 15 showsdetails of the oscillator and frequency divider 61 constituting thecontrol section 60, while the corresponding time chart is depicted inFIG. 16. An output signal P (period T of timing signal generator 62 inthe oscillator and frequency divider 61 are subjected to frequencydivisions by means of frequency divider 63 (frequency division ratio Ifrequency divider 64 (frequency division ratio I and frequency divider65 (frequency division ratio 1 so as to respectively obtain clock pulsesfor-the-time delay P having a period T (T,, T, X I clock pulses for thesweepsynchronizing signal P having a period T (T T, X I.) and analogswitch control pulses P having a period T (T,,,,, T,, X I,.).

Subsequently, the sweep-synchronizing-signal clock pulses P (period T.)are subjected to frequency division by means of frequency divider 66(frequency division ratio I,,), to thereby obtain the sweepsynchronizing pulses P, having a period T, (T, T X I,,). A frequencydivider 67 (frequency division ratio: I,,) is started with the sweepsynchronizing pulses P,,, so as to divide the period T of the time-delayclock pulses P and to thereby obtain the sweep synchronizing pulses Pwhich have a period T, and which are delayed by D (D T X 1,) over thesweep synchronizing pulses 1 The analog switch control pulses P (periodT are subjected to frequency division by means of a frequency divider 68(frequency division ratio I to obtain the display-section synchronizingsignal P (period I Ty T8, X

The horizontal synchronizing pulses P are obtained from the sweepsynchronizing pulses P With the imaging device of the foregoingconstruction, it becomes possible to pick out and image only an objectpresent at a distance aimed at, and it is possible to sharply lower thejamming output. According to experiments, a range resolution of 10cmcould be obtained with the device of the above embodiment.

While, with reference to FIG. 12, description has been made of theembodiment of providing the transmitting acoustic lens 15, it need notbe especially provided in case where the target object is distant.While, in the above embodiment, description has been made of the case ofdisplaying the received acoustic waves on the Braun tube, it may bereplaced with other recording means.

I claim:

1. An ultrasonic imaging system comprising:

a transmitter which transmits an output of various frequency components;

a band-shaped transmitting transducer which comprises a number oftransmitting elements arrayed in a predetermined direction, thedirections of polarization of the respective transmitting elements beingselected so as to be orthogonal to the arrayed direction and to bepolarized in a direction opposite to that of adjacent transmittingelements, and

common electrodes mounted on both surfaces of said transmitting elementsorthogonal to the polarization directions for applying the output ofsaid transmitter thereto, and which transducer radiates ultrasonic wavesat input frequencies from said transmitter in directions correspondingto said input frequencies, to scan a target object;

an acoustic lens for wave reception which converges said ultrasonicwaves received from said target object;

a receiving transducer which is divided into a plurality of receivingelements in a direction orthogonal to the scanning direction of saidultrasonic waves and on which said ultrasonic waves from said acousticlens are focused into an image; and

a receiver which subjects the outputs of said respective receivingelements of said receiving transducer to frequency analysis and whichdetects the respective frequency outputs.

2. An ultrasonic imaging system according to claim 1, further comprisingan acoustic lens for wave transmission which converges said acousticwaves from said transmitting transducer, to irradiate them on saidtarget object.

3. An ultrasonic imaging system according to claim 1, wherein saidreceiver comprises a first selector switch which selects said outputs ofsaid respective receiving elements, a frequency analyzer which subjectsthe outputs which have been selected by said selector switch tofrequency analysis and a second selector switch which selects therespective frequency outputs of said frequency analuzer.

4. An ultrasonic imaging system according to claim I, wherein saidreceiver comprises frequency analyzers which are provided incorrespondence with said outputs of said respective receiving elementsand which subjects said outputs of said receiving elements to frequencyanalyses, and a selector switch which selects the respective frequencyoutputs of said respective frequency analyzers.

5. An ultrasonic imaging system according to claim 1, wherein saidtransmitting transducer is curved towards said target object.

6. An ultrasonic imaging system comprising:

a transmitter which transmits an output varying in frequency with thelapse of time;

a band-shaped transmitting transducer which comprises a number oftransmitting elements arrayed in a predetermined direction, thedirections of polarization of the respective transmitting elements beingselected so as to be orthogonal to the arrayed direction and to bepolarized in a direction opposite to that of adjacent transmittingelements, and

common electrodes mounted on both surfaces of said transmitting elementsorthogonal to the polarization directions for applying the output ofsaid transmitter thereto, and which transducer radiates ultrasonic wavesat input frequencies from said transmitter in directions correspondingto said input frequencies, to scan a target object;

an acoustic lens for wave reception which converges and ultrasonic wavesreceived from said target object;

a receiving transducer which is divided into a plurality of receivingelements in a direction orthogonal to the scanning direction of saidultrasonic waves and on which said ultrasonic waves from said acousticlens are focused into an image; and

a receiver which detects the respective frequency components from saidrespective receiving elements and which selects, among said frequencycomponents, only components corresponding to the respective frequencieswhen the variations versus-time of the output frequencies of saidtransmitter are delayed by a predetermined period of time.

7. An ultrasonic imaging system according to claim 6, further comprisingan acoustic lens for wave transmission which converges said acousticwaves from said transmitting transducer, to irradiate them on saidtarget object.

8. An ultrasonic imaging system adcording to claim 6, wherein saidreceiver comprises a frequency sweep generator which generates frequencysignals having a fixed frequency difference from said output frequencyfrom said transmitter and with said variations-versustime of said outputfrequency delayed by said predetermined period of time, a mixer circuitwhich subjects the outputs of said respective receiving elements tofrequency conversion by said signals from said frequency sweepgenerator, a filter which derives a predetermined band component of anoutput of said mixer circuit, and an analog switch which selects theoutputs of said filter.

9. An ultrasonic imaging system according to claim 6, further comprisingdisplay means which displays the outputsof said receiver.

1. An ultrasonic imaging system comprising: a transmitter whichtransmits an output of various frequency components; a band-shapedtransmitting transducer which comprises a number of transmittingelements arrayed in a predetermined direction, the directions ofpolarization of the respective transmitting elements being selected soas to be orthogonal to the arrayed direction and to be polarized in adirection opposite to that of adjacent transmitting elements, and commonelectrodes mounted on both surfaces of said transmitting elementsorthogonal to the polarization directions for applying the output ofsaid transmitter thereto, and which transducer radiates ultrasonic wavesat input frequencies from said transmitter in directions correspondingto said input frequencies, to scan a target object; an acoustic lens forwave reception which converges said ultrasonic waves received from saidtarget object; a receiving transducer which is divided into a pluralityof receiving elements in a direction orthogonal to the scanningdirection of said ultrasonic waves and on which said ultrasonic wavesfrom said acoustic lens are focused into an image; and a receiver whichsubjects the outputs of said respective receiving elements of saidreceiving transducer to frequency analysis and which detects therespective frequency outputs.
 2. An ultrasonic imaging system accordingto claim 1, further comprising an acoustic lens for wave transmissionwhich converges said acoustic waves from said transmitting transducer,to irradiate them on said target object.
 3. An ultrasonic imaging systemaccording to claim 1, wherein said receiver comprises a first selectorswitch which selects said outputs of said respective receiving elements,a frequency analyzer which subjects the outputs which have been selectedby said selector switch to frequency analysis and a second selectorswitch which selects the respective frequency outputs of said frequencyanaluzer.
 4. An ultrasonic imaging system according to claim 1, whereinsaid receiver comprises frequency analyzers which are provided incorrespondence with said outputs of said respective receiving elementsand which subjects said outputs of said receiving elements to frequencyanalyses, and a selector switch which selects the respective frequencyoutputs of said respective frequency analyzers.
 5. An ultrasonic imagingsystem according to claim 1, wherein said transmitting transducer iscurved towards said target object.
 6. An ultrasonic imaging systemcomprising: a transmitter which transmits an output varying in frequencywith the lapse of time; a band-shaped transmitting transducer whichcomprises a number of transmitting elements arrayed in a predetermineddirection, the directions of polarization of the respective transmittingelements being selected so as to be orthogonal to the arrayed directionand to be polarized in a direction opposite to that of adjacenttransmitting elements, and common electrodes mounted on both surfaces ofsaid transmitting elements orthogonal to the polarization directions forapplying the output of said transmitter thereto, and which transducerradiates ultrasonic waves at input frequencies from said transmitter indirections corresponding to said input frequencies, to scan a targetobject; an acoustic lens for wave reception which converges andultrasonic waves received from said target object; a receivingtransducer which is divided into a plurality of receiving elements in adirection orthogonal to the scanning direction of said ultrasonic wavesand on which said ultrasonic waves from said acoustic lens are focusedinto an image; and a receiver which detects the respective frequencycomponents from said respective receiving elements and which selects,among said frequency components, only components corresponding to therespective frequencies when the variations-versus-time of the outputfrequencies of said transmitter are delayed by a predetermined period oftime.
 7. An ultrasonic imaging system according to claim 6, furthercomprising an acoustic lens for wave transmission which converges saidacoustic waves from said transmitting transducer, to irradiate them onsaid target object.
 8. An ultrasonic imaging system adcording to claim6, wherein said receiver comprises a frequency sweep generator whichgenerates frequency signals having a fixed frequency difference fromsaid output frequency from said transmitter and with saidvariations-versus-time of said output frequency delayed by saidpredetermined period of time, a mixer circuit which subjects the outputsof said respective receiving elements to frequency conversion by saidsignals from said frequency sweep generator, a filter which derives apredetermined band component of an output of said mixer circuit, and ananalog switch which selects the outputs of said filter.
 9. An ultrasonicimaging system according to claim 6, further comprising display meanswhich displays the outputs of said receiver.